Drying of yarn bodies



Patented Apr. 11, 1934 DRYING F YARN BODIES Ralph n. Carter, Johnson City, Tenn., 'assignor to American Glanzstofl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application July 16, 1932,

Serial No. 623,007

4 Claims. (01. 34524) My new invention has to do with a novel method for producing yarn, more especially yarn of artificial origin, by the so-called direct-spool process.

5 More particularly, my present; invention concerns a new and novel method of drying the yarn so that aneven shrinkage is produced.

However, the present method may also be applied to yarn spun or extruded upon the so-called collapsible spools, including slottedsnOQlS with collapsible holders and those spools whose shell or surface portion is adapted to contract, and

for filaments produced in cake form.

Artificial silk or rayon comes under the-general heading of hygroscopic material, that is, a material which is naturally constituted so that it is capable of absorbing or giving of! moisture at a certain rate of speed. This characteristic is employed by me in the method for drying artificial yarn set forth hereafter.

-It is the principal object of the present invention to set forth several methods of evaporating or extracting the moisture from yarn bodies derived from cellulosic solutions, such methods being designed so that an evenly shrunk yarn may be produced. Certain processes for the produc-' tion of an evenly shrunk yarn are covered by 00- pending applications, the property of the same assignee, namely, in co-pending applications S. N. 560,226,. (Bitter and Elssner); S. N. 548,474, (Bitter and Elssner); S. N. 560,225, (Elssner); S. N. ($20,724:, (Oppenlaender and Elssner); S. N. 562,427, (Elssner); S. N. 595,427, (Elssner); and S. N. 548,479, (Elssner). No attempt to claim the subject-matter of these other inventions is being made in the present instance, however, and

the present method is patentably distinct from these others.

The outline to be followed in the present process may be set forth as follows:

(1) Spools of untwisted yarn, after wet treatment, are loaded on or into a suitable conveying medium, preferably one which will permit free circulation of the air, or other drying medium, 4 in and around all portions of the spools, and the conveying medium is then placed into a drying chamber for the first drying operation.

(2) After drying, the yarn is removed from the spools, probably by twisting, and collected upon a. spool similar to that used in the first drymg operation. This rewinding should be accomplished so that the yarn which was originally on the outside of the spool body is'later on the inside, and the yarn which was formerly onthe inside is later on the outside. In certain instances no second drying may be necessary, and by proper regulation of the vapor pressure and temperature, as later described, commercially salable evenly-shrunk yarn maybe obtained. When collapsible spools or cakes, for example, are being dried, no second drying need necessarily be made. I have also secured salable yarn from a single drying on rigid spools.

(3) The yarn, upon spools which have been rewound, as pointed out above, is remoistened, bleached or otherwise wet treated, then placed in 'the drier for the second dryihg operation.

My new invention lies, broadly, when used in connection with rigid spools, in two dryings of the spooled yarn, as pointed out above, but the inventiveconcept lies in the method in which these dryings are accomplished. The two dryings are usually similar, and therefore a description of one of them should suffice to disclose my invention.

Method #1.As pointed out above, the yarn, upon rigid spools, is placed in a drying chamber while upon a suitable rack or other conveying medium. Heat is then applied to the drier with the yarn therein, a relative humidity closely approximating or equalling 100% being maintained until a predetermined temperature is reached. This temperature, at a relative humidity of 100%, is maintained for a certain length of time, until the yarn body is heated uniformly throughout. These conditions prevent the removal of any moisture from the yarn body. I have found that good results may be accomplished if the relative humidity is maintainedat 100% until a temperature of 60-70 C. is reached. Ordinarily'the temperature may be maintained at this figure, together with the 100% humidity, for from 30 minutes to 1 hour. Then a gradual decrease in the relative humidity, or wet bulb depression, is occasioned. This naturally decreases the vapor pressure of the drying medium in the drier, and the drying or removal of the moisture from the yarn body commences. The relative humidity is therefore reduced at such a rate that the moisture coming to the outside surface of the yarn body is evaporated at the same rate as the rate at which it comes to the surface. This is explained by the fact that the internal vapor pressure of the yarn body is slightly higher than the external vapor pressure, and the former is continually forcing the moisture therein to the surface of the yarn body, and the circulating drying medium, being at a slightly lower vapor pressure, absorbs the moisture asit comes to the surface of the yarn body. The reduction of rela- 110 -to their hygroscopic nature. twisted yarn on spools may give up or absorb tive humidity below 100% is usually continued to a point which will dry the-yarn to a given moisture content by weight. For example, if a yarn body with a moisture content, by weight, of from 4 to 6% is desired, the relative humidity during the drying may be reduced to approximately 25%. At 70 C. dry bulb, the difference between the internal and external vapor pressures is usually very slight. It must be understood, however, that I do not desire to limit my invention to the exact percentages, temperatures, and times given, since the process, of itself, is essentially novel, and I wish to be limited in the present method, and those alternative methods following, only by the scope of the appended claims.

Method #2.The yarn is placed in the drying chamber in the manner outlined in the discussion of Method #1. Heat is applied, as in Method #1, at a relativehumidity of 100%, until the yarn-body is thoroughly and uniformly heated throughout. The relative humidity is then reduced, as above, at a given rate of speed in excess of the speed at which the yarn body will give up its moisture. Thus, as outlined above, a certain amount of drying is accomplished. This drying may be continued until the yarn has, for example, a moisture content by weight of approximately 75%. The yarn is thus not dried to the extent named in Method #1. Then the relative humidity is again increased to 100% for a certain length of time. I have found that a time of approximately 2 hours gives good results. This stepresults in the moistening of the outside layers to some extent. The reduction of relative humidity is then repeated, as at first, until a lower relative humidity is reached, namely approximately 50%. These steps or cycles may then be repeated until the proper moisture content of the yarn is reached. In each of the sequence of steps or cycles, the relative humidity is lowered a slight amount below the relative humidity reached in the preceding cycle. Any

number of cycles may be employed during the complete drying operation as some yarn bodies require different treatment from others owing For instance, un-

moisture differently from twisted yarn on spools,

depending on the amplitude of windand the.

tension used when winding the yarn on the spools. Method #3.-This method is a modification of that in Method #2, above. It has been found preferable, in some cases, instead of increasing thewet bulb temperature to the dry bulb-temperature, to decrease the dry bulb to the wet bulb reading, at the end of the said cycles, because it has been found that at a lower temperature a better moistening effect may be obtained at 100% relative humidity. The wet and dry bulb readings are then raised together to approximately 70 C. and 100% relative humidity, and the gradual depression of the wet bulb reading restarted. As examples of the points to which respective bulb reading may be depressed in order to give good results, I may mention from 70 C. to 45 C.

Method #4.The yarn upon rigid spools is placed in the drying chamber, and brought to 100% relative humidity for a certain length of time, as indicated'in Methods #1, 2, and 3. The temperature at which the yarn is maintained at first, in the manner indicated in the other methods, is approximately 45 C. The dry bulb temperature is then increased to a given point, for example, 70 C. and the wet bulb reading decreased to a given point, for example, 40 C.,

of water.

which causes a rapid evaporation of the moisture from the yarn body. I have found that these increments of 25 0. increase and 5 C. decrease in the readings are equivalent to approximately 25% relative humidity. The drying medium in the drier is maintained in this condition until a certain percentage of the moisture, by weight, is removed from the yarn, for example, until from 50% to 75% of the moisture by weight has been removed. Then the dry bulb temperature is depressed and the wet bulb temperature increased until the 100% relative humidity is again reached. At this point of the operation it will be foundthat the outer layers of yarn, which have been dried to a certain extent, pick up moisture from the circulating drying medium. This is, therefore, more or less a remoistening operation, since the outer layers of the yarn have moisture deposited thereon at a comparatively lower temperature, i. e., a temperature actually lower than the drying temperature. The drying of the moisture from the filaments is then accomplished in the manner pointed out in the preceding methods.

In order to clarify the above description with respect to the wet and dry bulb readings, the following description of wet and dry bulb hygrometers is given. The cooling effect of evaporation is employed by these hygrometers or thermometers, and use is made of them in determining the amount of moisture in the drying medium employed. )Ihese hygrometers comprise a pair of ordinary thermometers which are similar, except that there is a piece of muslin tied about the bulb of one. The muslin is in contact with a wick, the lower end of which is in a vessel By virtue of the capillary action of the wick and muslin, the bulb is kept moist. The moisture evaporating from the bulb cools it, causing this thermometer to read several degrees cooler than the other one. If the air is very dry, this evaporation will be very rapid, and the difference between the reading of the two thermometers will be large; whereas, if,the air is almost saturated with moisture, the evaporation will be slow, and the two thermometer readings will vary but slightly.

The velocities of the air or other drying medium which may be used also plays an important part in the drying or extraction of moisture from the yarn bodies to be treated. For example, when air is circulated at a relatively high velocity, e. g., 500 .feet a minute it has a tendency to defeat the purpose of the method since it practically blows the moisture from the yarn bodies. When very low velocities are used, the drying requires too much time. I have found that velocities of from 25 to 400 feet per minute may be used. In carrying out the processes just described, I regulate the velo'city'of the drying medium according to the nzoisture content of the yarn bodies being dried, e c.

Having now set forth my invention as required by the patent statutes, what I desire to claim is:

1. The process of drying artificial silk yam wound on spools comprising the steps of placing the moisture-laden yarn bodies in a drying chamber, heating the said yarn bodies with a circulating drying medium having a relative humidity of approximately 100%, maintaining a relative humidity in the drying chamber at approximately the saturation point of the drying medium until the yarn is uniformly heated throughout, and then gradually reducing the relative humidity of the drying medium at such a rate that the moisture coming to the outside surface of the yarn body is evaporated at the same rate as the rate at which the moisture comes to the surface.

2. The process of drying artificial silk yarn wound on spools comprising the steps of placing the moisture-laden yarn bodies in a drying chamber, heating the said yarn bodies with a circulating drying medium having a temperature of from 60 to '70 degrees C. and which has a relative humidity of approximately 100%, maintaining this temperature and relative humidity at approximately the saturation point of the drying medium until the yarn is uniformly heatedthroughout, and then gradually reducing the.

relative humidity of the drying medium at such a rate that the moisture coming to the outside surface of the yarn body is evaporated at the same rate as that rate at which it comes to the surface.

3. A process of drying artificial silk wound on spools comprising steps of placing moisture-laden yarn bodies in a drying chamber, heating the said yarn bodies with a circulating drying medium having a dry and wet bulb temperature of approximately 60 to 70 degrees C., maintaining this relative humidity until the yarn body is uniformly heated throughout, then reducing the wet bulb temperature at such a rate that the moisture on the surface of the yarn body is evaporated at a faster rate than the rate that said moisture comes to the surface of the yarn body, continuing this last step until the outside layers of theyarn body are approximately dry, then decreasing the dry bulb temperature to the wet bulb temperature.

then raising the wet and dry bulb temperature together until 60 to '10 degrees is again reached,

repeating the above cycle with the exception that successive lowerings of the wet bulb temperature are greater than those of the preceding cycles,

and continuing these cycles until an approximately dry state of the yarn body is reached which is uniform throughout.

4. The process of drying artificial silk yarn wound on spools comprising the steps of placing the moisture-laden yarn bodies in a drying chamber, heating the said yarn' bodies with a circulating drying medium having a temperature of approximately 45 degrees C. and which has a relative humidity of approaching 100%, maintaining this temperature and relative humidity which approaches a saturation point of the drying medium until the yarn is uniformly heated throughout, increasing the dry bulb temperature to '10 degrees C. while decreasing the wet bulb temperature to 40 degrees C., maintaining these wet and dry bulb temperatures until the outer layers of the yarn body are approximately dry, then increasing the relative humidity to 100% by decreasing the dry bulb temperature to 45% and increasing the wet bulb temperature to 45 degrees, maintaining this 100% humidity until a portion of the dried layers have again becomemoistened, then repeating this raising and lowering of the relative humidity until an approximately dry state of the yarn body is reached which is uniform throughout.

RALPH CARTER. 

